The present invention relates to an optical writing head, particularly to an optical writing head using a self-scanning light-emitting element array.
A light printer head, i.e. an optical writing head comprises a light-emitting element array in which a plurality of light-emitting elements are arrayed in one line. When an optical writing head is structured by using a light-emitting diode (LED) array, for example, as a light-emitting element array, about 7200 LEDs are arrayed in one line for an optical writing head of 600 dpi (dots per inch) which prints on an A3 size paper. In this optical writing head, an electrode of each LED is electrically connected to an electrode of a driving IC. A wire bonding is usually used for such electrical connection. An IC for driving n LEDs generally converts n serial data into n parallel data, thereby controlling the light emission condition of the n LEDs.
Therefore, the number of signal lines derived from the optical writing head is equal to that of the driving ICs except the signal lines for power supply and timing. In the case of excess number of signal lines in such structure, a particular driving IC is provided for distributing (serial-parallel conversion) data to m driving ICs so that the number of signal lines may be decreased by a factor of m.
In this manner, as the conventional optical writing head has lines the number thereof is equal to that of LEDs, it is difficult to interface with an external part otherwise the number of lines to be derived is decreased by serial-parallel conversion with the particular driving IC. The particular driving IC is mounted on the same substrate on which the LED array is mounted, then this causes the problem in that the width of the head, i.e. the width in a direction perpendicular to the direction of LED arrangement becomes large. There is also a problem in that the particular driving IC for serial-parallel conversion is to be provided in the head, resulting in a high production cost.
The inventors of the present invention have interested in a three-terminal light-emitting thyristor having a PNPN-structure as an elements of the light-emitting element array, and have already filed several patent applications (see Japanese Patent Publication Nos. 1-238962, 2-14584, 2-92650, and 2-92651.) These patent publications have disclosed that a self-scanning function for light-emitting elements may be implemented, and further have disclosed that such self-scanning light-emitting element array has a simple and compact structure for the light source of a printer, and has smaller arranging pitch of thyristors.
The inventors have further provided a self-scanning light-emitting element array having such structure that an array of light-emitting thyristors having transfer function as a shift register is separated from an array of light-emitting thyristor having writable function (see Japanese Patent Publication No.2-263668.)
The object of the present invention is to provide an optical writing head in which the number of bus lines to be derived may be decreased by using a self-scanning light-emitting element array.
One point light-emitting type of self-scanning light-emitting element array chip used in an optical writing head comprises the following basic structure.
That is, the one point light-emitting type of self-scanning light-emitting element array chip comprises;
a transfer element array having such a structure that a plurality of three-terminal transfer elements each having a control electrode for controlling threshold voltage or current are linearly arranged, the control electrodes of the transfer elements neighbored to each other are connected via an electrically unidirectional element, a power supply line is connected to all the control electrodes via respective load resistors, and n-phase (n is an integerxe2x89xa72) clock lines are connected to one of two terminals other than the control electrode of each of the transfer elements, repeatedly at intervals of n transfer elements, and
a light-emitting element array having such a structure that a plurality of three-terminal light-emitting elements each having a control electrode for controlling threshold voltage or current are linearly arranged, each control electrodes of the light-emitting element array is connected to the control electrodes of the corresponding transfer element, and a line for applying a write signal connected to one of two terminals other than the control electrode of each of the light-emitting elements is provided.
According to a first aspect of the optical writing head of the present invention, a plurality of chips described above are linearly arranged, a start pulse bus line is commonly connected to the respective chips, n-phases clock pulse bus lines are commonly connected to the respective chips, and write signal bus lines are separately connected to the respective chips.
According to a second aspect of the optical writing head of the present invention, current limiting resistors to be connected to the start pulse bus line, n-phase clock pulse bus lines, and write signal bus lines are included in the chip, in the optical head of the first aspect.
According to a third aspect of the optical writing head of the present invention, current limiting resistors to be connected to the n-phase clock pulse bus lines are included in the chip, in the optical writing head of the first aspect.
According to a forth aspect of the optical writing head of the present invention, a buffer IC is inserted in each of the n-phase clock pulse bus lines, in the optical head of the third aspect.
According to a fifth aspect of the optical writing head of the present invention, a two point light-emitting type of self-scanning light-emitting element array chip is used. In this aspect, a start pulse bus line is commonly connected to the respective chips, n-phases clock pulse bus lines are commonly connected to the respective chips, two write signal bus lines are separately connected to the respective chips, the two write signal bus lines are alternately connected to the light-emitting elements in each chip.
According to a sixth aspect of the optical writing head of the present invention, a plural light-emitting type of self-scanning light-emitting element array chip is used. The plural light-emitting type of self-scanning light-emitting element array chip comprises;
a transfer element array having such a structure that a plurality of three-terminal transfer elements each having a control electrode for controlling threshold voltage or current are linearly arranged, the control electrodes of the transfer elements neighbored to each other are connected via an electrically unidirectional element, a power supply line is connected to all the control electrodes via respective load resistors, and n-phase (n is an integerxe2x89xa72) clock lines are connected via current limiting resistors to one of two terminals other than the control electrode of each of the transfer elements, repeatedly at intervals of n transfer elements,
a light-emitting element array having such a structure that a plurality of three-terminal light-emitting elements each having a control electrode for controlling threshold voltage or current are linearly arranged, each control electrode of the light-emitting element array is connected to the control electrode of the corresponding transfer element at intervals at n elements, and a line for applying a write signal connected via a current limiting resistor to one of two terminals other than the control electrode of each of the light-emitting elements is provided.
In an optical writing head structured by linearly arranging the chips described above, start pulse bus line are separately connected to the respective chips, n-phases clock pulse bus lines are commonly connected to the respective chips, and a write signal bus line is commonly connected to the respective chips.
According to a seventh aspect of the present invention, in an optical writing head using one light-emitting type of self-scanning light-emitting element array chip, m (m is an integerxe2x89xa72) start pulse bus line are repeatedly connected to the respective chips, n-phases clock pulse bus lines are commonly connected to the respective chips, write signal bus lines are separately connected to every m chip neighbored to each other, and current limiting resistors to be connected to the start pulse bus line, n-phase clock pulse bus lines, and write signal bus lines are included in the chip.
According to a eighth aspect of the present invention, in an optical writing head using one light-emitting type of self-scanning light-emitting element array chip, the plurality of chips are divided into groups each thereof including m (m is an integerxe2x89xa72) chips, an end bonding pad of one chip is connected to the start pulse bonding of next chip in one group of chips, a start pulse bus line is commonly connected to a first chip of the respective groups, n-phase clock pulse bus lines are commonly connected to the respective chips, and write signal bus lines are separately connected to all the chips of the respective groups.
According to a ninth aspect of the present invention, in an optical writing head using the plural light-emitting type of self-scanning light-emitting element array chip, start pulse bus lines are separately connected to every m (m is an integerxe2x89xa72) chips neighbored to each other, one-phase m clock pulse bus lines are repeatedly connected to the m chips neighbored to each other, another-phase clock pulse bus lines are commonly connected to the respective chips, and a write signal bus line is commonly connected to the respective chips.